Environment Canada meteorologist Lisa Coldwells says much of the southern interior will be in the mid to high 30s by the weekend.
On Saturday Lytton is forecast to hit 40 C. By Sunday temperatures are expected to climb as high at 39 C in Kamloops and Castlegar, and 38 C in Kelowna and Osoyoos.
Temperatures in Vancouver are forecast to peak at 29 C on Sunday and 34 C in Abbotsford.
"We're toying again with record temperatures," said Coldwells, referring to the highs forecast for the southern Interior.
That kind of heat can cause dehydration and even heat stroke, according to Dr. Rob Parker with Interior Health.
"Seniors and young children especially can be affected by the heat. And it would be worthwhile checking in on them and seeing if they need anything to help them cope."
And it's not only temperatures that are going up. Fire information officer Kelsey Winter says the fire danger rating in the southern Interior of the province is expected to soar.
"We are expecting that danger rating to climb as the week continues and that will put us into extreme in various areas."
The heat wave is expected to last until mid next week.
More hot, dry weather ahead
Coldwells has said previously that there is a strong chance of higher than normal temperatures this summer across British Columbia because of a trend of warmer water in the Pacific Ocean that influences weather in the Pacific Northwest.
Meanwhile the B.C. River Forecast Centre has issued an extreme low flow advisory for several creeks and rivers on Vancouver Island, saying conditions now are more typical of late-August.
The centre blames the low water levels on the low snow pack and precipitation levels, along with warmer than average temperatures.
And with little rain and continued warm weather, the levels are expected to continue to decrease over the next several weeks.
The list of affected rivers includes several that are below minimum lows recorded for this period, including Tofino Creek, Browns River, Gold River and Koksilah River.